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Chapter 5

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Ashley Waggoner Denton

Chapter 5- Sensation and Perception Sensation: the sense organs’ responses to external stimuli and the transmission of these responses to the brain Perception: the processing and interpretation of sensory signals, it results in an internal representation of that stimulus Sensory coding: sensory organs’ translations of stimuli’s physical properties into neural impulses 1. Transduction: sensory receptors pass impulses to connecting neurons when they receive physical/chemical stimulation 2. Connecting neurons transmit info to brain in the form of neural impulse pass by thalamus cerebral cortex- incoming neural impulses interpret it as sight, smell, sound, touch or taste (Perception) • Qualitative info: light change from green red, different receptors respond to different stimuli • Quantitative info: light goes brighter same receptors fire more rapidly * Coarse coding: sensory qualities coded by few receptors that respond to broad range of stimuli Psychophysics: Ernst Weber and Gustav Fechner- examines our psychological experiences of physical stimuli • Examines how much physical energy is require for our organs to detect stimulus, how much change is required before we notice change Sensory thresholds • Absolute threshold: minimum intensity of stimulation that must occur before you experience a sensation • Difference threshold: minimum amount of change required for a person to detect a difference between 2 stimuli • Difference threshold ↑’s as stimulus becomes more intense= Weber’s law (difference is based on proportion of original stimulus vs. actual difference) Ex: picking up pen stapler vs. textbook and slightly heavier textbook Signal Detection Theory • States that detecting a faint stimulus requires a subjective judgement- not just all-or- none response • Ex: radiologist- detecting tumour- knowledge of patient’s history, age, consequence of his prognosis, all affect his judgement • Any trial in which participants judge whether an event occurs has 1 of 4 outcomes: 1. Hit: signal present and observer detects it 2. Miss: signal present, observer misses it 3. False alarm: observer detects signal, no signal 4. Correct rejection: no signal, no detection * compare hit rate with false alarm rate participant’s sensitivity to signal (validity) Response bias: Amount of evidence needed for observer to say signal is present Ex: radiologist needs a lot of evidence to make sure tumour is there vs. doctor looking at broken bone (having a cast on not as big of a deal if mistake vs. cancer treatment) Sensory adaptation • Decrease in sensitivity to a constant level of stimulation or noticing stimulus is gone after constant presence • Ex: working in library construction outside, stop noticing it after awhile Basic Sensory Processes 1. Gustation: sense of taste • Taste buds cranial nerve • Supertasters: people who experience intense taste sensations (genetics) • Cultural factors influence taste as well- mothers pass down eating preferences on to offspring in womb 2. Olfaction: sense of smell • Most direct route to brain (NO RELAY IN THAMALUS) • Odorants pass into nasal cavity olfactory receptors in olfactory epithelium transmit signal to olfactory bulb (brain centre for smell) olfactory nerve • Prefrontal cortex- process whether smell is good or bad • Amygdala- processes intensity of smell 3. Hepatic sense- touch • Conveys sensations of temperature, pressure, pain and sense of where limbs are in space • Hepatic receptors- sensory neurons on skin’s outer layer  transmit signal to trigeminal nerve (above neck) or spinal nerve (below neck 2 types of nerve fibres associated with pain, depending on amount of myelination 1. fast fibres: fast, sharp pain (protective) 2. slow fibres: chronic, dull, steady pain (recuperation) Gate control theory of pain • pain is perceptual experience rather than simply response to nerve stimulation • states that for us to experience pain, pain receptors must be activated and a neural “gate” in the spinal cord must allow to signals through to the brain • pain can be blocked at spinal cord level before gets to brain by larger sensory nerve fibres ex: distraction, numbing cream at dentist closes gate vs. worrying focusing on painful stimulus opens gate • pain is both a sensory experience and an emotional response (processed by 2 different regions in brain) nd 3. audition- sense of sound perception (2 to vision) • change in vibrations in air pressure produce sound waves • amplitude- determines its loudness • frequency-determines its pitch • sound waves outer ear- make eardrum vibrate middle ear- cause ossicles and oval window to vibrate creates pressure waves in inner’s ear’s fluid, bends hair cells cause neurons to fire auditory nerve • auditory localization: we use both intensity and timing of sounds to locate where they are coming from (if sound reaches right ear first, know it’s coming from right) 4. Vision Cornea: first structure light interacts with, where most refraction occurs (change in direction of light) Pupil: dark circle in back of eye Iris: coloured muscle, contract/relax control amount of light lets in Retina: where all photoreceptive cells are, coverts light into AP’s “projection screen” • Cones: colour vision • Rods: sensitive to hard dark/bright area is Fovea: within retina, where most colour-sensitive photoreceptive cells are Optic nerve: where all cell axons leave the eye • Blind spot: no photoreceptive cells Optic chiasm: ½ info crosses over to other side of brain o Optic nerve optic chiasm thalamus 1 visual cortex Cornea flips world • R side of visual world projects onto L side of eye/retina • L side of L eye stays on same side • L side of R eye crosses over • R side of world left cerebral hemisphere • receptive field: region of visual space to which neurons in the primary visual cortex are sensitive • consists of centre and a surrounding region- light is shined at centre, neural firing increases, when light is directed to surrounding region, neural firing decreases, no light cells fire at baseline rate • lateral inhibition: visual process in which adjacent photoreceptors tend to inhibit one another (emphasizes changes in visual stimuli- sensitive to edges, where objects end) • Hermann grid • Colour of light is determined by its wavelength
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